nvmem: zynqmp: Added zynqmp nvmem firmware driver

This patch adds zynqmp nvmem firmware driver to access the
SoC revision information from the hardware register.

Signed-off-by: Nava kishore Manne <nava.manne@xilinx.com>
Acked-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>